Formal charge:
When do you use it? How is it calculated?
Formal charge is used in chemistry to evaluate the distribution of electrons in a molecule or polyatomic ion. It helps to determine the stability and reactivity of these species.
Formal charge is calculated using the following equation:
Formal Charge = Valence Electrons (in the neutral atom) - Non-bonding Electrons - 1/2 * Bonding Electrons
To calculate the formal charge, follow these steps:
1. Determine the total number of valence electrons in the neutral atom. This can be found by referring to the periodic table and considering the group number for main group elements.
2. Count the number of non-bonding (lone pair) electrons on the atom.
3. Count the number of electrons shared in covalent bonds with other atoms. Divide this number by 2 since each bond involves two electrons.
4. Subtract the sum of non-bonding and bonding electrons from the total valence electrons.
Once you calculate formal charges for all atoms in a molecule or polyatomic ion, you can evaluate their distribution to identify any atoms that carry a positive or negative charge.
Note: The sum of formal charges in a neutral molecule should be zero, while in an ion, it should be equal to the ion's overall charge.